1. Field of the Invention
This invention relates to an additive composition for use in motor fuels. More specifically, this invention relates to a motor fuel additive composition which is effective to reduce deposits on the intake valves of an internal combustion engine.
2. Description of Related Information
The combustion of a hydrocarbon motor fuel in an internal combustion engine leads to the formation and accumulation of deposits on intake valves. Intake valve deposits interfere with valve closing and eventually will lead to valve burning. Such deposits interfere with valve motion and valve seating, reduce the volumetric efficiency of the engine and reduce the maximum power obtainable. Valve deposits may be produced from, among other things, thermally and oxidatively unstable fuel or from lubricating oil oxidation products. The hard carbonaceous deposits produced collect in the tubes and runners that are part of the exhaust gas recirculation (EGR) flow. These deposits are believed to be formed from exhaust particles which are subjected to rapid cooling while mixing with the air-fuel mixture. Reduced EGR flow can result in engine knock and in nitric oxide, NO.sub.x, emission increases. It would, therefore, be desirable to provide a motor fuel composition which minimizes or overcomes the formation of intake valve deposits.
Another problem common to internal combustion engines is the formation and accumulation of deposits on various parts of the combustion chamber as well as on the fuel intake and exhaust system of the engine. The presence of deposits in the combustion chamber seriously reduces the operating efficiency of the engine. First, deposit accumulation within the combustion chamber inhibits heat transfer between the chamber and the engine cooling system. This leads to higher temperatures within the combustion chamber, resulting in increases in the end gas temperature of the incoming charge. Consequently, end gas auto-ignition occurs, causing engine knock. In addition, the accumulation of deposits within the combustion chamber reduces the volume of the combustion zone, causing a higher than design compression ratio in the engine. This, in turn, can also lead to engine knocking. A knocking engine does not effectively utilize the energy of combustion. Moreover, a prolonged period of engine knocking can cause stress fatigue and wear in pistons, connecting rods, bearings and cam rods of the engine. The phenomenon noted is characteristic of gasoline powered internal combustion engines. It may be overcome by powering the engine with a higher octane gasoline which resists knocking. This need for a higher octane gasoline as the engine accumulates operating time has become known as the engine octane requirement increase (ORI) phenomenon. It is particularly advantageous if a fuel additive's contribution to engine ORI can be substantially reduced or eliminated by preventing or modifying deposit formation in the combustion chambers of the engine.
The present invention provides a gasoline detergent additive composition which reduces the level of deposits on intake valves with no significant contribution to combustion chamber deposits.